This invention relates to coaxial connectors for connection to coaxial cable plugs and more particularly to a coaxial cable-connector assembly for connection to a Super High Frequency (SHF) electrical circuit element for conducting SHF signals to or from the element and to which a conventional coaxial cable plug can connect.
Heretofore, a coaxial cable-connector assembly for direct connection of the cable part thereof to a high frequency circuit element operating in the SHF range of 18 to 20 GHz and higher has been provided to users in the form of a coaxial cable four to six inches long with a coaxial connector at each end. Each connector is adapted for threadably engaging the plug of a conventional coaxial cable. The user makes two cable-connector assemblies of this by cutting the cable at a suitable point between the two connectors. Each of these assemblies is used by first removing the outer conductor and dielectric a ways back from the cut end to expose the center conductor which the user then attaches to the high frequency circuit element, thereby providing a coaxial port for that connection to which the plug of a conventional coaxial cable can be connected. Thus, the product provides the user with two SHF coaxial ports to the circuit.
At SHF frequencies of 18 to 20 GHz, or higher, the cable of the assembly is as small as Number 047, 50 ohm cable (0.047 inches in diameter) and the threads of the connector attached to the cable are 1/4 inch by 36 threads per inch and so the connector is also quite small. Clearly, connecting such a small cable and connector requires the engagement of the very fine, wire-like (about 0.010 inches in diameter), center conductor of the cable with the center conductor of the connector so that the two fit together in intimate electrical and mechanical contact, poses some problems in fabrication. One of the problems is to align the connector center conductor with the connector outer conductor housing so that they are in perfect coaxial alignment, so when the connector receives the inserted end of the cable that is attached thereto, the fine, wire-like center conductor of the cable slides inside the connector center conductor. Any slight shift in the position of the connector center conductor relative to the connector housing may upset this alignment.
For example, such a coaxial cable-connector assembly is used to provide a very low impedance electrical connection to SHF circuit elements such as a YIG filter. These assemblies are sometimes called "YIG cable assemblies". They provide a connection to the YIG filter for a conventional coaxial cable plug external of the YIG circuit. As mentioned above, the cable assembly is usually provided with a length of cable four to six inches long and a connector attached to each end. The user cuts the cable to the length desired and uses each half to make a connection for a conventional coaxial cable plug. Each is used by baring the fine, wire-like center conductor a sufficient length for attachment to the YIG filter.
In the past, such a cable assembly has been made by inserting a bared end of the cable with the wire-like center conductor thereof projecting, into an accommodating end of the connector so that the center conductor of the cable (hopefully) fits inside a spring finger at that end of the connector center conductor. Then, the outer conductor of the cable is soldered to the connector housing. Following that, epoxy is applied around the connector center conductor, dielectric and housing through a hole provided therein to fix them in position and so insure that radial and axial alignments of the connector center conductor, dielectric and housing are maintained during use. This technique is sometimes referred to as "epoxy captivated contacts".
At the assembly of the cable and connector, the bared end of the cable that is inserted into an accommodating part of the connector, is inserted before the captivating epoxy is applied around the connector parts to fix their positions, and then the cable is soldered to the connector. The captivating epoxy cannot be applied before inserting the cable and soldering, because the heat of soldering would so effect the epoxy that it would not be effective to fix the parts in position. At this assembly, when the bared cable is inserted into the connector accommodation, any misalignment of the connector spring finger and cable center conductor will at least force either or both out of position with respect to the outer conductors and so will likely impair electrical performance, or, at worse, bend the very thin cable center conductor so that it either does not contact the connector center conductor spring finger or it shorts to the connector housing. As a consequence, fabrication of such cable-connector assemblies suffers a high rejection rate.